The present invention relates to an eye image pickup apparatus for acquiring an image of a human eye and an entry/leave management system utilizing the eye image pickup apparatus.
An iris image is used for personal authentication for entry/leave management and a user of an ATM (Automatic Teller Machine), a computer and a cellular phone. A human iris pattern is formed in his/her childhood and differs from person to person and from the left eye to right eye of a person. Thus the iris pattern data is excellent for personal identification.
As eye image pickup apparatus for acquiring an iris pattern is known to identify the position of an eye by using a camera with a wide field of view and to picking up an image of the eye while moving the field of view of a telephotographic camera, for example, Japanese Patent Publication No. H10-137225. Such apparatus, however, requires a large-scale configuration and has limited applications. In particular, application to portable apparatus such as a cellular phone is virtually impossible.
A conventional eye image pickup apparatus includes an objective lens 1 and an image pickup element 2 such as a CCD with a half mirror or cold mirror 21 arranged in front of the objective lens 1, as shown in FIG. 3. The cold mirror is a mirror which reflects a visible light and transmits an infrared light and can be used for shooting with illumination of an infrared light. Apparatus in FIG. 3 can correctly shoot an image of an eye of a user of the apparatus when the eye of the user is on an optical axis 5 of a shooting optical system thus the eye image is reflected at a specific location of the mirror. The apparatus requires a mirror 21 larger than the lens 1. This makes it difficult to apply the apparatus to portable apparatus. Also, when an eye of a user of the apparatus is not reflected in the mirror 21 as shown in the figure, the user does not know in which way he/she should move. In case the dominant eye of the user is different from the eye reflected in the mirror 21, the user cannot make correct positioning.
An apparatus has been devised where first edge means and second edge means are provided in the field of view of a telephotographic camera of eye image pickup apparatus for acquiring an iris pattern for the user to position his/her eye, for example, Japanese Patent Publication No. H10-505180. Both the first and second edge means are arranged in front of the lens of the telephotographic camera thus requires a large-scale apparatus arrangement thus making difficult the application to portable apparatus such as a cellular phone.
Then, an eye image pickup apparatus is proposed in U.S. Patent Application Publication No. 2002/0005893 A1, the eye image pickup apparatus solves the aforementioned problems in a conventional apparatus and can correctly shoot an eye image in a short time with a simple configuration which can be mounted on portable apparatus.
FIG. 4 shows a basic configuration of the proposed eye image pickup apparatus which includes an objective lens 1, an image pickup element 2 such as a CCD constituting an image pickup section, a shading unit 3 as a mark and a light guide section 4. The shading unit 3 shades part of a shooting optical path and provided concentrically with an optical axis 5 of a shooting optical system. The shading unit 3 is preferably provided on a lens and is preferably in the shape of a circle. The light guide section 4 guides a visible light from a visible light source (not shown) toward the objective lens 1 at a midpoint in the shooting optical path. Guide position of the visible light is closer to the image pickup element than the shading unit 3. The cross section of a visible light thus guided has a similar shape to the shading unit 3 and its center coincides with the optical axis 5. Area ratio of the cross section of the visible light to the effective optical path cross section of the shooting optical system is approximately equal to or slightly larger than that of the shading unit 3 to the effective optical path cross section of the shooting optical system.
In the apparatus in FIG. 4, when the eye is on the optical axis 5, the shading unit 3 and the guiding visible light 6 have an approximately equal area so that they look like an annular eclipse as shown in FIG. 5A. The image shot by the image pickup element 2 has an eye in the center as shown in FIG. 5B. It is possible to accurately recognize an iris pattern by capturing a shot image in this state.
On the other hand, when the position of the eye is not on the optical axis 5, the image of the shading unit and the guiding visible light look like a partial eclipse in FIG. 5C. The image shot by the image pickup element 2 looks like FIG. 5D. A favorable iris pattern is not obtained in this state so that it is necessary to move the position of the eye. The direction the eye should move in is easily recognized by FIG. 5C.
As shown in FIG. 6, the light guide section 4 is arranged at a position closer to the image pickup element 2 than the middle point a of the objective lens 1 and the image pickup element 2. In case the light guide section 4 is arranged closer to the objective lens 1 (for example position b), when the center of an eye to be shot (right eye R in the figure), the shading unit and the light guide section 4 are on the same straight line, the light guide section 4 is seen from the other eye (left eye L in the figure), which makes it more difficult to position the eye. On the other hand, when the light guide section 4 is brought closer to the image pickup element 2, the light guide section is not seen from the left eye L so that it is easier to position the eye. In particular, a person who cannot close one eye (wink) can easily position his/her eye.
The shading unit 3 in FIGS. 4 and 5 is provided on an optical axis of a shooting optical system but may be provided in an annular way on the periphery of the lens 1. That is, the periphery of the lens 1 may be shaded in an annular way. FIG. 7 is an example of an annular shading unit by way of a lens catch 13 provided on the lens. In the apparatus in FIG. 7, when an eye of a user is on the optical axis, the opening of the lens catch 13 and the guiding visible light 6 looks concentric. An image shot by the image pickup element 2 has an eye in the center as shown in FIG. 8B. When the eye is not on the optical axis, the visible light 6 looks partially and the image shot by the image pickup element 2 is as shown in FIG. 8D. In FIGS. 8A and 8C, a numeral 18 represents the opening of the lens catch 13. Providing an annular shading unit in this way allows a shading unit to be manufactured by changing the dimensions of the lens catch 13 and thus can be manufactured at lower cost than a shading unit on an optical axis.
FIG. 9 shows a general configuration of an example of the proposed eye image pickup apparatus. An objective lens 1 is attached on a one end of a lens-barrel 8 by way of a lens catch 13. On the other end of the lens-barrel, an image pickup section 7 having a CCD 2 as an image pickup element is provided. The specific structure of the image pickup section 7 may be changed as required depending on the structure of a device to be employed so that the details will be skipped. In the center of an inner surface of the lens-barrel 8 of the objective lens 1, a shading unit 3 in a circular shape with its center aligned with the optical axis 5 is provided. The shading unit 3 can be formed by gluing a black sticker onto the objective lens 1. Alternatively, the shading unit 3 can be formed by applying a black paint onto the objective lens 1.
By providing a white or yellow sticker or a white or yellow paint as a shading unit 3, the position of the shading unit 3 is made easier to locate. This is because the shading unit 3 in a fair color is easier to find although the shading unit 3 in a dark color makes it difficult to locate the shading unit 3.
An optical fiber 9 inserted from the side face of the lens-barrel 8 is provided inside the lens-barrel 8. On the optical fiber 9 at the end outside the lens-barrel 8, an LED 10 constituting a visible light source is provided to face the end face of the optical fiber 9. A visible light emitted from the LED 10 may be of any color but preferably green considering the human identification ability. The other end of the optical fiber 9 is bent toward the objective lens 1 so that the end face 11 will be perpendicular to the optical axis 5 and its center coincides with the optical axis 5. Thus, the visible light from the LED 10 serves as a guiding visible light 6 toward the objective lens 1 via the end face 11. The side face of the optical fiber 9 is painted black in order to decrease the influence on the image pickup element 2.
Area ratio of the end face 11 of the optical fiber 11 to the effective optical path cross section of the shooting optical system is set approximately equal to or slightly larger than that of the shading unit 3 to the effective optical path cross section of the shooting optical system. When setting is made this way, the shading unit 3 and the guiding visible light 6 look like an annular eclipse shown in FIG. 5A as seen on the optical axis external to the lens-barrel 8. The larger the area ratio of the end face 11 of the shading unit 3 to the effective optical path cross section of the shooting optical system, the better its visibility becomes but the brightness of the shot image decreases. An area ratio of about 5% is preferable.
An infrared light is appropriate for shooting an iris. Thus an infrared light generator (not shown) is preferably provided on the periphery of the objective lens 1 of the lens-barrel 8 to shoot an infrared image. In this case, providing a visible light cutoff filter 12 before the image pickup section 7 in order to eliminate the influence of the visible light on the CCD 2 can acquire a more accurate image.
In case the shading unit is annular, the dimensions of the lens catch 13 are changed and a sticker or a paint is not applied.
FIG. 10 shows a general configuration of an example of the proposed eye image pickup apparatus. The same numerals are used to show the same components in FIG. 9 and corresponding description is omitted. The configuration in FIG. 10 differs from the shooting optical system in FIG. 9 in that the lens-barrel 17 is bent approximately at a right angle and an optical path bending mirror 14 for bending the shooting optical path is provided at the bent section of the lens-barrel 17. The surface of the optical path bending mirror 14 facing the objective lens 1 is provided with a reflective film 15 by way of aluminum evaporation except for the periphery of the optical axis 5.
On the side face of the lens-barrel of the optical path bending mirror 14 opposite to the objective lens 1, an LED 10 is provided on the extension line of the optical axis 5. A visible light is introduced as a guiding visible light 6 toward a transmitting section 16 of the optical path bending mirror 14. The transmitting section 16 is formed so that the cross section perpendicular to the optical axis 5 will be in the shape of a circle and functions as a light guide section for a visible light. An optical fiber may be provided in between in order to efficiently introduce a visible light from the LED 10.
Area ratio of the cross section of the transmitting section 16 perpendicular to the optical axis 5 to the effective optical path cross section of the shooting optical system is set approximately equal to or slightly larger than that of the shading unit 3 to the effective optical path cross section of the shooting optical system. When setting is made this way, the shading unit 3 and the guiding visible light 6 look like an annular eclipse shown in FIG. 5A as seen on the optical axis external to the lens-barrel 8. An area ratio of about 5% is preferable as the area ratio of the shading unit 3 to the effective optical path cross section of the shooting optical system.
When the transmitting section 16, shading unit 3 and the center of an eye are on the same line, it is possible to shoot the eye in the center of a shot image. However, to know whether the image is focused, it is necessary to check on the monitor screen. Focusing without checking the image on the monitor screen is possible in case the color of the transmitting section changes between when focus is achieved and when it is not. Thus, providing a dual-color LED at the rear of the transmitting section 16 and changing the color of the LED between when focus is achieved and when it is not allows focusing without checking the image on the monitor screen.
FIG. 11 shows a general configuration of another example of the proposed eye image pickup apparatus. The same numerals are used to show the same components in FIGS. 9 and 10 and corresponding description is omitted. The apparatus in FIG. 11, same as that in FIG. 10, is characterized in that the lens-barrel 17 is bent approximately at a right angle and an optical path bending mirror 14 for bending the shooting optical path is provided at the bent section of the lens-barrel 17. The apparatus in FIG. 11 differs from that in FIG. 10 in that the dimensions of the lens catch 13 are made smaller than those of the apparatus in FIG. 10 and a sticker or a paint is not applied.
As mentioned earlier, according to the proposed eye image pickup apparatus, it is possible to grasp the eye moving direction by way of the alignment of the mark with the guiding visible light seen when the user looks through the objective lens. It is thus possible to accurately acquire an iris image even when the image pickup apparatus is downsized so as to be incorporated into portable apparatus. The mark and the light guide section are provided on or behind the lens so that an additional element for positioning an eye keeps the apparatus configuration compact. This configuration is easy to use when the user has accustomed to it, like the case where a same person uses a PC every day regularly when he/she logs in to the system.
Like a case where a great number of people use the apparatus, not necessarily frequently, while they are standing, such as when the invention is applied to an entry/leave management system, the following problems occur. First, although it is easy to guide an eye of a user to the center of the opening 18 as long as the guiding visible light is in the opening 18 of the lens catch 13 as shown in FIG. 8A, it is difficult to determine in which direction the user should move his/her eye in case the eye is at a different height. Another problems is how to focus the eye image in shooting. It is possible to guide the user by changing the color of the transmitting section 16 between when focus is achieved and when it is not, as in the apparatus shown in FIGS. 10 and 11. However, a great number of people who use the apparatus not necessarily frequently, such as users of an entry/leave management system, cannot easily determine whether to approach or step back. That is, there is no means for making rough guidance so that it is not easy for an unaccustomed person to correctly position his/her eye to be shot on the shooting path.